What is currently the most elaborated part of linguistic comparison?

What is currently the most elaborated part of linguistic comparison?
2. What is the second factor of scientific comparative works?
3. What does the general definition of Linguistic typology imply?
4. What are the main principles classifying words into parts of speech?

1. Comparative linguistics, or comparative-historical linguistics is a branch of historical linguistics that is concerned with comparing languages to establish their historical relatedness. Genetic relatedness implies a common origin or proto-language and comparative linguistics aims to construct language families, to reconstruct proto-languages and specify the changes that have resulted in the documented languages. To maintain a clear distinction between attested and reconstructed forms, comparative linguists prefix an asterisk to any form that is not found in surviving texts. A number of methods for carrying out language classification have been developed, ranging from simple inspection to computerised hypothesis testing. Such methods have gone through a long process of development.

2. Comparative research is a research methodology in the social sciences exemplified in cross-cultural or comparative studies that aims to make comparisons across different countries or cultures. A major problem in comparative research is that the data sets in different countries may define categories differently (for example by using different definitions of poverty) or may not use the same categories.
3. Linguistic typology is the study the ways in which the languages of the world vary in their patterns. It is concerned with discovering what grammatical patterns are common to many languages and which ones are rare. Typologists look at variation in all domains of grammar, including phonetics, phonology, morphology, syntax, and semantics. Typology is a very active research area of the Department of Linguistics, underlying the theoretical research on syntax, morphology, and semantics.
4. Parts of speech are grammatical classes of words which are distinguished on the basis of four criteria:
- semantic;
- morphological;
- syntactic;
that of valency (combinability)
1) Meaning. Each part of speech is characterized by the general meaning which is an abstraction from the lexical meaning of the constituent word. Thus, the general meaning of nouns is thingness (substance), the general meaning of verbs is action, state, process; the general meaning of adjectives — quality, quantity. The general meaning is understood as categorial meaning of the class of words.
Semantic properties of every part of speech find their expression in their grammatical properties. If we take "to sleep, a night sleep, sleepy, asleep" they all refer to the same phenomena of the objective reality but belong to different parts of speech as they have different grammatical properties.
Meaning is supportive criterion in the English language which only helps to check purely grammatical criteria - those of form and function. Глокая куздра штэка будланула бокра и кудрячит бокрёнка. V. V. Vinogradov Green ideas sleep furiously.
Such examples though being artificial help us to understand that - grammatical meaning is an objective thing by itself though in real speech it never exists without lexical meaning.
2) Form, (morphological properties) The formal criterion concerns the inflectional and derivational features of words belonging to a given class. That is the grammatical categories they possess, the paradigms they form and derivational and functional morphemes they have. With the English language this criterion is not always reliable as many words in English are invariable, many words have no derivational affixes and besides the same derivational affixes may be used to build different parts of speech.(e.g. "~ly": quickly , daily , weakly(n.)). Because of the limitation of meaning and form as criterion we should rely mainly on words' syntactic functions (e.g. "round" can be adjective, noun, verb, preposition).
3) Function. Syntactic properties of any class of words are: combinability (distributional criterion), typical syntactic functions in a sentence. The three criteria of defining grammatical classes of words in English may be placed in the following order: syntactic, distribution, form, meaning (Russian: form, meaning, syntactic distribution). Parts of speech are heterogeneous classes and the boundaries between them are not clearly cut especially in the area of meaning. Within a part of speech there are subclasses which have all the properties of a given class and subclasses which have only some of these properties and may even have features of another class. So a part of speech may be described as a field which includes both central (most typical) members and marginal (less typical) members. Marginal areas of different parts of speech may overlap and there may be intermediary elements with contradicting features (modal words, statives, pronouns and even verbs). Words belonging to different parts of speech may be united by common feature and they may constitute a class cutting across other classes (e.g. determiners or quantifiers).